The present invention generally relates to protective headgear. More specifically, the present invention relates to protective headgear that includes an improved shell construction.
In the prior art, there are many different types of helmets. Helmets used by football players, bicyclists and others engaged in sports typically have a hard outer shell that covers energy-absorbing material, also known as padding.
For example, bicycle helmets typically have a hard plastic outer shell that covers expanded polystyrene. Polystyrene absorbs energy by developing multiple micro-fractures throughout its structure. Once a polystyrene helmet develops micro-fractures it ceases to provide impact protection (i.e., such helmets are unusable after a single impact). Also, football helmets typically have a dense polyethylene outer shell that covers polypropylene pads capable of absorbing multiple impacts. The pads may also be air or liquid filled. Other helmets, such as those used by soldiers, typically have a metal or composite shell; that is able to protect a soldier's head from certain types of high-energy impacts.
Also, helmets typically have a retention system to secure the helmet in proper position on the user's head. The straps commonly used for bicycle helmets are difficult to adjust, resulting in many bicyclists wearing helmets improperly positioned and providing limited protection. Football, hockey and lacrosse helmets also typically further include protection for the face, such as wire cage or impact resistance plastic. This face protection is also attached directly to the helmet construction.
The helmet shape and the extent to which it covers the head are important design considerations. Helmets are shaped differently depending on the use to which the helmet is to be put and the energy level of the impacts the user might experience. For example, football helmets are typically designed to protect the top, sides and front of the user's head while the wire cage protect the wearer's face.
Performance standards have been developed for certain types of helmets. For bicycle helmets, for example, the Snell B-95 Bicycle Helmet Standard involves a series of performance tests. A helmet passes the impact portion of the Snell test if it prevents a head from decelerating at a rate in excess of 300 G's when subjected to a specific test impact. The Snell 300 G's standard does not assure that a rider wearing a helmet meeting that standard will not suffer serious head injury. Head and brain injuries occur at deceleration levels well below 300 G's; also, riders can experience impacts that result in head deceleration levels above 300 G's. Similar testing is conducted and standards are set in place for other sports, such as football and lacrosse.
The governing bodies of sports such as football and lacrosse in which helmets must be able to maintain their energy-absorbing performance after multiple impacts require that these sport helmets meet standards such as those developed by the National Operating Committee on Standards for Athletic Equipment (NOCSAE). In these standards performance test require that for the specified impact conditions the acceleration of the headform fitted with the given helmet not exceed a power-weighted integral of acceleration-time curve value of 1200 SI.
Headgear construction for high impact sports, such as football, is of particular concern to ensure that the head is adequately protected. The head can be thought of as having three components: the skull; the brain, which consists of compressible matter; and the fluid filling the skull and in which the brain floats. Neither the skull nor the fluid is compressible; the brain, however, is compressible and, when forced against the skull, does compress, bruising brain tissue and perhaps causing hemorrhaging. When the skull experiences an impact, the force is transmitted through the skull and fluid; the inertia of the fluid results in the brain moving in a direction opposite from that of the force applied to the skull. If that force is applied suddenly (i.e., there is an impact) and is substantial enough, the brain moves through the fluid and strikes the inside of the skull at a point roughly opposite to the area of the skull that sustains the impact.
When the brain strikes the skull with moderate force, the brain tissue in the area of the brain that hits the skull is compressed and bruised. That typically results in a temporary cessation of nervous function (i.e., a concussion).
When the skull is subjected to a more substantial impact, the brain typically hits the inside of the skull at a higher speed; a larger area of brain tissue is compressed and damaged and brain hemorrhaging is common (i.e., contusion results). If minimal hemorrhaging occurs, the individual may experience symptoms similar to those of a concussion. More substantial hemorrhaging may result in a loss of blood supply to the brain and even death.
When the energy level of the impact to the skull is substantial enough, the skull fractures. When it does, some of the impact energy is dissipated. A fracture may be either linear or localized. A linear fracture, the simpler of the two, is essentially a straight line crack. A localized fracture is one in which multiple fractures occur in a single area. In such a fracture, it is common for skull bone material to be displaced; the displacement can result in bone material penetrating brain tissue, causing hemorrhaging and swelling.
FIG. 1, a perspective view and FIG. 2, a cross-sectional view through the line 2-2 thereof, show a prior art headgear construction 10, which may be a football helmet. The helmet 10 is shown to include typical prior art headgear construction, which includes an outer shell 12 as well as padding 14 that resides between the shell 12 and the wearer's head 16. A wire cage 18 is provided on the front of the helmet 10 to protect the face of the wearer 16.
The profile of the shell 12 of prior art headgear 10 is generally flat. A cushioning material 14, such as foam and air bladders are typically placed between the outer shell 12 and the user's head 16 to serve as an inner liner. These additional layers help absorb impact to help prevent trauma to the head 16. Due to the configuration of a flat outer shell 12, however, the impact is distributed over a fairly small area resulting in less than desired impact absorption. The use of the cushioning liner materials 14 is critical in prior art helmets 10 to ensure effective impact absorption. Thus, the primary focus in prior art helmets 10 in the improvement of the cushioning material 14 and the configuration thereof for better impact absorption not the outer shell configuration 12 and materials.
Prior art headgear 10 must focus on the improvement of the padding layer 14 and its construction because the localized impact area of known shells 12 cause the impact load to be concentrated in a relatively small area. FIG. 3 illustrates such impact concentration. When this occurs, the padding 14a in the region of the localized impact at shell portion 12a takes on the burden of cushioning the load and deforms accordingly. If the impact is great enough, which occurs frequently in football, the padding 14 cannot sufficiently handle the impact and, as a result, the shell 12 bottoms out against the wearer's head in the region 12a due to full compaction of padding 14a therebetween thereby increasing the risk of head injury. Essentially, when the padding is fully compacted when at a distance of D at 14a and shell 12 bottoms out at 12a, it can no longer provide the required cushioning. As a result, it is critical that the padding 14 not bottom out when the shell 12 is impacted.
To illustrate this, FIG. 12, a graph of acceleration against compression, shows that as the linear compresses and begins to bottom out, the resulting headform acceleration increases rapidly. Thus there is a need to reduce compression of the linear by spreading the impact force over a greater area that results in lower head acceleration for a given impact.
Moreover, repeated localized impacts which are not spread out over the surface of the shell an absorbed across the pads, will cause deformation so significant that the pad fails in that area thereby degrading the overall integrity of the headgear and increasing risk of injury.
Thus, prior art helmets are extremely limited as to how much impact it can sustain due to the nature of the (locally flat—of course its generally spherical) flat profile of the outer shell and cushioning intermediate layer. The only profiling of the outer shell, in known helmets, are solely for aesthetic purposes, which include vents, grooves and other stylized elements. These elements are not used for functionally improving the impact absorption capability or rigidity of the helmet.
Therefore, there is a need for a helmet that can better prevent head injuries by improving the configuration and design of the outer shell of the helmet. There is a further need for a helmet that has a shell construction that can better spread the load of an impact across the surface of the shell and through to a wide pad area thereunder. There is a need for a headgear construction that eliminates the bottoming out of padding to improve performance, integrity and life of the headgear. There is also a need for a headgear construction that can stiffen the overall performance of the shell.